English CD version of the game
In the original, it looks like there's some kind of transparency effect or similar on the laser diffusion field. In ScummVM, it's a uniform dark gray.
Comparing the two screenshots, I also noticed that colours seem slightly darker in ScummVM (I've seen similar in games where the original doesn't use even 8 bits per colour, but I haven't checked if that's what's going on here) and that there's a dark line at the top of the scene in ScummVM. The latter is probably the only thing worth looking into.
The problem seems to be in Scene600::Smoke::getFrame(). Transparency isn't taken into account when copying the pixels
Looks right to me.